it is in the exhaust system, before the muffler.
Plugged catalytic converter?
2. one before the cat. converter and one after it, near tailpipe
Torque converter going bad
The O2 sensors are threaded into the exhaust system, one before the catalytic converter and one after the cat.
the upstream o2 sensor is mounted in the exhaust before the catalytic converter and the downstream sensor is after the cat. conver.
cat converter is getting plugged
On a 2001 Chevrolet Malibu, the oxygen sensor is typically located in the exhaust system. There are usually two sensors: one upstream (pre-catalytic converter) and one downstream (post-catalytic converter). The upstream sensor is generally found near the exhaust manifold, while the downstream sensor is located further along the exhaust pipe, before the catalytic converter. You may need to lift the vehicle for better access to the sensors.
The 2001 Chevrolet Malibu has 12 valves.
The 2001 Chevrolet Malibu has a V6 engine.
Assuming that you are referring to the downstream oxygen sensor, that will be the one located after the catalytic converter (the exhaust side, not the engine side).
In 2001 the Ram 2500 diesel did not come with a cat. it has a resonator and a muffler. the thing under the cab that looks like a cat is actually a resonator. so no they are not required
The 2001 Chevrolet Malibu has overhead valves (OHV).